Browse Prior Art Database

BI-DIRECTIONAL FIBRE-OPTIC COUPLER

IP.com Disclosure Number: IPCOM000024704D
Original Publication Date: 1981-Oct-31
Included in the Prior Art Database: 2004-Apr-02
Document File: 4 page(s) / 147K

Publishing Venue

Xerox Disclosure Journal

Abstract

A bi-directional coupler system 10 is shown in Figure 1 and includes a first transmitter 12 which transmits optical radiation at frequency ;i and which is injected into flat end surface 14 of single optical fibre 16, the injected radiation being detected at the far end of fibre 16 by detector 18. Similarly, a second transmitter 20 transmits radiation at a second frequency h which is injected into the far end of optical fibre 16 and emerges through end face 14 of optical fibre 16 onto receiver or detector 22 for detecting the i"\ radiation.

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XEROX DISCLOSURE JOURNAL

BI-DIRECTIONAL FIBRE-OPTIC COUPLER Proposed Classification David A. Grafton U.S. C1. 350/96.18
Eric 8. Hochberg
CI. Int. Ronald E. Purkis GO26 5/12

U

FIBER

FIG. 1

'

CROSST AL W

   RADIATION "NEAR END"

Volume 6 Number 5 September/October 1981 249

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BI-DIRECTIONAL FIBRE-OPTIC COUPLER (Cont'd)

A bi-directional coupler system 10 is shown in Figure 1 and includes a first transmitter 12 which transmits optical radiation at frequency ;i and which is injected into flat end surface 14 of single optical fibre 16, the injected radiation being detected at the far end of fibre 16 by detector 18. Similarly, a second transmitter 20 transmits radiation at a second frequency h which is injected into the far end of optical fibre 16 and emerges through end face 14 of optical fibre 16 onto receiver or detector 22 for detecting the i"\ radiation.

In order to minimize the cross talk inherent in the coupler shown in Figure 1, an investigation into the nature of cross talk sources was initiated. (Cross talk refers to all radiation in the "near end" transmitters' spectrum which appears in the output of the "near end" receiver.)

The major cross talk components identified fall into two categories: cross talk power originating at the fibre/air interface and cross talk power originating from within the bulk of fibre 16.

The first component is believed to result from a Fresnel reflection at the fibre/air interface. With no geometric isolation, this component is entirely within the field of view of the detector. The second component is attributed to Rayleigh scattering mechanisms within the bulk of the fibre. As this component emerges from the fibre in a manner identical to the emerging radiation desired to be detected, it can only be suppressed by spectral means. The first component however can be isolated by geometric/spatial means. The present invention, as shown in Figure 2, augments the spectral suppression provided by a bandpass filter means with geometric isolation. That is, if the emitter radiation is injected in the form of a near-collimated beam of size comparable to the filter core diameter, at normal incidence the Fresnel reflection component in principle is arranged to pass back through a pinhole and thereby out of the field of view of the detector. The fraction that does not pass through the pinhole is within the field of view of the detector but is subject to the spectral suppression provided by a bandpass filter means located downstream.

Referring to Figure 2, a laser transmitter 12, emitting relatively monochromatic radiation centered at wavelength A 1, transmits its radiation to col...